Description of the Prior Art
As is known, the majority of zig-zag sewing machines have comprised, for very many years, a cradle having, generally, the form of a support pivoted about a substantially vertical axis, the support being caused by a mechanism to tilt laterally with an alternating movement and comprising two supports, for example two superpositioned arms, with which there are associated two coaxial bearings adapted to receive a needle bar mounted for axially sliding displacement within the bearings.
Whether it is a question of bearings formed by the walls themselves of axial openings machined directly in the body of the arms, or, on the contrary, of sockets driven into such openings, easy and precise axial sliding of the needle bar depends essentially on one condition: the machining of the openings must be such that on its completion, the openings in question must occupy a rigorously aligned position.
It will be understood that the observance of such a condition may be the source of innumerable problems as much in regard to the machining itself as in respect of the mounting of the assembly: machine builders have therefore been compelled to require to develop particularly elaborate and thus costly machining and finishing processes for the parts.